1. Field of the Invention
This invention relates to a method and apparatus for inputting graphics by hand, using a two-dimensional input device such as a tablet, and displaying the results of said input.
2. Background Information
Graphical systems which use a pen as an interface to input handwritten characters have become increasingly important as the cost of liquid crystal displays decreases and their resolution increases.
Conventional systems which support handwritten input can be generally classified as either batch processing systems or interactive processing systems. In batch processing systems, preprocessing is applied to drawings written on paper to recognize topology of line segments. Examples of these systems are those which deal with flowcharts and wiring diagrams. In contrast, the interactive processing systems recognize figures. However, in these interactive systems, the line drawings which can be input are limited to line segments whose size allows them to be segmented or "cut out." That is, input is performed by writing (with one stroke) a primitive unit. Recognition is performed by matching the input unit with a basic figure such as a square, circle or character. Examples of the methods used in the interactive systems are described in Kojima,et al., "On-line Handwriting Figure Recognition by the Adjacent Segments Structural Analysis Method," Information Articles Journal, August 1987 and in the Published Unexamined Japanese Patent Application No. 226387/1990.
In actual practice, however, when a user desires to input a free curve, it is difficult for that user to input the entire desired curve at one time. It is more natural to create a curve by drawing short line segments, repeating the process by trial and error until the entire curve is completed--much in the same way that a designer sketches. As a result, a graphic input method for drawing a free curve which can connect short, sketched line segments (such as result from drawing the curve on paper) is desirable.
As costs are reduced and resolution increased for liquid crystal display tablets, new applications which use interactive sketch-like graphical input systems that employ pen input will be developed. In such applications, an input method as described above--that is input of short line segments for drawing in a sketch style--will be important.
In the prior art, methods of generating a curve consisting of short line segments using parabolic blending techniques was known. One such method is described in A. W. Overhauser, "Analytic Definition of Curves and Surfaces by Parabolic Blending," Technical Report No. SL 68-40, Ford Motor Company Scientific Laboratory, May 8 (1968). However, in Overhauser's method, the number of objective points is limited according to the degrees of parabolas to be blended, and only so-called short line segments can be treated. Accordingly, it would be difficult to use this method to create one continuous line segment from a plurality of input line segments of differing length--i.e., both long or short--as would be performed by a user actually drawing on paper).
In summary, many handwriting input systems have been proposed which place emphasis on recognition of a figure, drawing or character. These systems do not address an interface technique which would allow line segments to be input in the same way that a user create these segments by hand on paper, although this feature is essential for interactive systems.